The present invention concerns a process of preparation of amino functionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%. The invention also concerns polymers of such type, a rubber composition and a tire casing containing said polymers.
Applicant has described, in French Patent FR-A-2,294,186, a process of polymerization of conjugated dienes or of copolymerization of conjugated dienes, either with other conjugated dienes or with vinylaromatic compounds. The examples of polymers obtained, which appear in that document, present 1,4-trans linkage contents covering a wide range, extending from 24% to 90%.
This process consists essentially of reacting the monomers in the presence of a catalytic composition made up of an organolithium initiator and of a co-catalyst. The latter comprises a barium or strontium compound and an organometallic compound of IIB or IIIA group metals of the periodic classification of elements.
More precisely, said organolithium initiator can be, for example:
an aliphatic organolithium, such as ethyl lithium, n-butyl lithium, isobutyl lithium, sec-butyl lithium, ter-butyl lithium, isopropryl lithium, n-amyl lithium and isoamyl lithium;
an alkene organolithium, such as allyl lithium, propenyl lithium and isobutenyl lithium;
a living polymer, such as polybutadienyl lithium, polyisopropenyl lithium and polystyryl lithium;
a polymethylene dilithium, such as 1,4-dilithiopentane, 1,5-dithiopentane and 1,20-dilithioeicosane;
an aromatic organolithium, such as benzyl lithium, phenyl lithium and 1,1-diphenylmethyl lithium;
a polylithium obtained from an aryl-substituted ethylene compound, the latter being, for example, 1,1-diphenylethylene, trans-stilbene and tetraphenylethylene;
a radical ion, such as lithium naphthalene, lithium anthracene, lithium chrysene and lithium diphenyl;
a derivative substituted by one or more alkyls.
The said barium or strontium compound is, for example, a hydride, or a mono- or polyfunctional organic acid, such as an alcoholate.
As for said organometallic compound of IIB or IIIA group metals, it may be, for example a dialkyl zinc or cadmium, a halogenated or nonhalogenated organoaluminum, an organoborium or a dialkyl aluminum hydride.
One can also cite U.S. Pat. No. 4,996,273, which discloses a process of anionic preparation of polybutadiene having a 1,4-trans linkage content ranging between 82% and 91%, consisting of using an organolithium initiator, a barium, strontium or calcium compound and a trialkylaluminum compound having at least 13 carbon atoms.
It will be noted that neither the FR-A-2,294,186 nor U.S. Pat. No. 4,996,173 mentions obtaining functional polymers.
Also known, from European Patent EP-A-661,298, is a process of preparation of diene polymers which are amino-functionalized and comprise an alkoxysilane group. These polymers are, notably, characterized by a 1,2 linkage content ranging between 14% and 16%, that is, by an overall 1,4-cis and 1,4-trans linkage content ranging between 84 and 86%, which implies a 1,4-trans linkage content very appreciably below 80%, in the order of 60% at most.
This process consists, notably, of using, on the one hand, a lithium amide base catalytic initiator and, on the other, a randomizing agent making it possible to control the 1,2 linkage content in the polymers prepared, and then of reacting the living polymer obtained with an alkoxysilane compound.
Said initiator is, for example lithium hexamethylene imide.
As for said randomizing agent, it can be an ether, an orthodimethoxybenzene, an alkali metal complex and a phosphorous acid ketone or triester, oxygenated derivatives of an alkali or alkaline earth metal, like lithium, sodium, potassium, calcium or barium, or even a tertiary amine.
All of the examples of preparation appearing in EP-A-661,298 refer to processes for obtaining styrene-butadiene copolymers. These processes consist of directly adding the said initiator and the said randomizing agent to the polymerization medium, which consists of styrene and butadiene monomers and of a polymerization solvent.
Concerning the anionic preparation of polymers containing an amino function, European Patent EP-A-590,491 can also be cited. This document mentions the use of an aminolithium initiator consisting, for example, of hexamethyleneimine, notably, for obtaining styrene and butadiene copolymers presenting a narrow distribution of molecular weights. The copolymers obtained are characterized by vinyl linkage content of at least 34.9%, that is, by 1,4-trans and 1,4-cis linkages equal to not more than 65.1%, which implies an even lower 1,4-trans linkage content.
The present invention provides a process for preparing of amino functionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%. The invention also concerns polymers of such type, a rubber composition and a tire casing containing the polymers.
The process of preparation according to the invention involves polymerizing at least one diene monomer by means of a lithium catalytic system, which consists essentially of at least one hydrocarbon solvent, one compound A of a IIIA group metal, one compound B of an alkaline earth metal and one aminolithium initiator C.
Amino functionalized diene polymers with high 1,4-trans linkage content according to the invention are such that the amino function, situated at the end of the polymer chain, is a tertiary amino function, the rate of functionalization of said polymers being equal to or greater than 50% and the 1,4-trans linkage content being equal to or greater than 70%.
A rubber composition vulcanizable with sulfur according to the invention is such that it contains at least said polymer.
A tire casing according to the invention is such that it contains said composition.